LED modules in COB technology (COB=chip on board) are sealed mostly with cover resins based on epoxy resins. Such modules are for example known from EP 1347517 and EP 1352431. Although the use of silicones is mentioned in the patent claims (e.g. also in EP 1347517) such modules are not yet used in practice. The main reason for this is the known insufficient adhesive force of these silicone materials.
There are also known modules with adhered on lenses; also here there are preferably used as adhesives systems based on epoxides. These materials normally develop a very good adhesive force. However, a significant disadvantage of the epoxides is their restricted endurance in the use of blue LEDs. The emitted light of a wavelength of ca. 460 nm leads to a rapid yellowing of these resins, which in turn leads to a fall-off of the brightness of the LED modules. On operation in damp surroundings only an insufficient dampness protection is provided for the component by the epoxide, the endurance in the case of temperature change loading is unsatisfactory.
Besides the configurations described above numerous further constructions are known for LED modules and luminaires. In some of these configurations silicones are again mentioned as casting materials or filler materials. By way of example attention is directed to the patents U.S. Pat. Nos. 6,504,301, 6,590,235, 6,204,523 and DE 10261908. In none of these documents, however, is the adhesion of the silicones on the materials used discussed. In some of the described constructions the mechanical stability of the structure is ensured by additional structural measures (e.g. in U.S. Pat. No. 6,504,301).
In other configurations, however, silicone gels are put to use, but due to their nature can afford no mechanical protection for the semiconductor and its bonding wires. A gel can therefore always only be used in connection with other structural measures.
In the use of epoxides as a casting resin for photodiodes, e.g. as optical sensor in air conditioning controllers, the insufficient light-fastness of the resins is also a limiting factor for the operating life.